Differently from polymer molded products such as films, fibers, injection molded products and extrusion molded products, polymer microparticles are used for modification and improvement of various materials by utilizing their large specific surface area and their spherical shape. Their major uses include modifiers for cosmetics, additives for toners, additives for paints, additives for molded products and light diffusing agents for films (JP-A-2010-8757 and JP-A-2005-220035).
Typical examples of such versatile polymer microparticles include acrylic polymer particles and polystyrene polymer particles which can be produced by a generally known method such as emulsification polymerization and suspension polymerization, and which are used for the above-described various applications.
On the other hand, polycarbonates are known as a polymer having high heat resistance, high refraction index and high weather resistance compared to acrylic polymers and poly-styrenes, and are used for a wide variety of applications in resin moldings. However, there are only few publications that disclose how to form polycarbonate into a microparticle shape, and the major method to obtain powder-like products was the crushing method (JP-A-2011-26471).
On the other hand, as a known method of producing polymer microparticles, a method using emulsion is disclosed in WO 2009/142231 A1. However, although attempts to produce polycarbonate-based polymer microparticles were being made, the obtained particles had an uneven surface and did not have acceptable properties such as particle flowability which is required for cosmetics and the like (WO '231).
Further, a method is disclosed in which polycarbonate is melted in silicone oil, mixed by homogenizer, and thereafter cooled to produce polycarbonate particles. However, the polycarbonate particles obtained by that method contain not only a small proportion of spherical smooth-surface microparticles but also a huge proportion of fiber-like polycarbonates, and it was difficult to isolate microparticles from them. In other words, it was not possible to obtain polycarbonate-based polymer microparticles having acceptable properties such as flowability by using that method (JP-A-2001-213970).
It could therefore be helpful to provide a method of producing polycarbonate-based polymer microparticles, particularly real spherical polycarbonate-based polymer microparticles having a smooth particle surface and being suitable for cosmetics, films having a function of diffusing light and the like.